An international traveler — silhoutted against a closed door — arrive at Logan International Airport in Boston. (Brian Snyder/Reuters)

U.S. Customs and Border Protection has detained an Iranian cancer researcher and his family — including a baby — for more than 24 hours at Boston’s Logan International Airport and will force them to leave the country, federal officials and a grass-roots organization said Tuesday.

Mohsen Dehnavi, a 32-year-old father of three, was traveling to Massachusetts on an exchange visa to conduct postdoctoral research at Boston Children’s Hospital, a world-renowned facility affiliated with Harvard University.

“This individual was deemed inadmissible to the U.S. based on information discovered during the CBP inspection,” CBP spokeswoman Stephanie Malin said in a statement. “As is customary with individuals denied entry to the U.S., they will depart on the next scheduled flight.”

The episode occurred just over two weeks after the Supreme Court granted the Trump administration permission to carry out a modified version of the president’s entry ban on certain citizens from Iran and five other majority-Muslim countries.

Federal officials said Dehnavi’s imminent expulsion had nothing to do with the travel ban. But they would not say why he was being deported, citing privacy laws.

Malin provided only the broad outlines under which someone could be barred from entering the United States.

“In order to demonstrate that they are admissible, the applicant must overcome ALL grounds of inadmissibility including health-related grounds, criminality, security reasons, public charge, labor certification, illegal entrants and immigration violations, documentation requirements, and miscellaneous grounds,” she said.

Boston Children’s Hospital had urged customs officials to release Dehnavi and his family and dispatched a lawyer to the airport.

“Dr. Dehnavi is a visiting research scholar on a J-1 visa coming to Boston Children’s with his wife and three children,” hospital spokesman Rob Graham emailed earlier in the day. “Boston Children’s hopes that this situation will be quickly resolved and Dr. Dehnavi and his family will be released and allowed to enter the US.”

Trita Parsi, president of the National Iranian American Council, a grass-roots organization based in Washington, said he received a message at 2 a.m. Tuesday from a friend of Dehnavi’s who had been waiting since Monday to pick up the family at the Boston airport.

Parsi said the friend, Mohammad Rashidian, also a Boston Children’s Hospital researcher, told him that federal officials said Dehnavi had a documentation issue but did not explain what it was. Parsi said that Rashidian had not been able to communicate with Dehnavi and that relatives in Iran are “worried sick.”

He wondered why Dehnavi and his family were allowed to board a flight to the United States if there was a paperwork issue.

“How could he get this far and be denied here?” he said. “They’re not being forthcoming.”

Logan International Airport was the scene of massive protests after Trump imposed his initial travel ban on Jan. 27. The order was soon halted by federal courts and then revised by the administration in March. The American Civil Liberties Union and others have challenged the ban as discriminatory, but the administration says it is trying to shore up national security.

The Supreme Court allowed a modified version of the travel ban to take effect this month until it can hear the case when it reconvenes in October. The ban restricts travel temporarily for visitors and refugees who are citizens of Iran and five other majority-Muslim countries: Libya, Somalia, Sudan, Syria and Yemen.

Parsi said that even without the travel ban, the Trump administration appears to have restricted travel from the six countries. He said visa issuances to Iranians, the largest affected group, are down. He has heard that visa interviews are being canceled and not rescheduled.

Under the administration’s new rules, grandparents, grandchildren, uncles, aunts, cousins and fiances of people in the United States are not allowed to enter the country.

Parsi asked how barring a cancer researcher such as Dehnavi, or grandmothers, improves national security.

“This is actually making America less safe,” he said. “It’s taking our eyes off the real problem.”

Dehnavi was traveling on a visa that allows thousands of foreign visitors a year to experience U.S. “society and culture and engage with Americans,” according to the State Department’s website.

Abigail Hauslohner contributed to this report.